The present application is based on and claims priority from Japanese Patent Application 2002-55814, filed Mar. 1, 2002, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a stator of an ac generator for a vehicle such as a truck, a passenger car or the like.
2. Description of the Related Art
As the idling speed of vehicles is reduced recently to reduce fuel consumption, the rotation speed of vehicle ac generators is also lowered. On the other hand, the output power of the vehicle generators has to be increased in order to operate various vehicle safety devices.
It is well known that the output power of a vehicle ac generator can be increased if the space factor of a stator winding to stator core""s slots is increased, which reduces the resistance of the stator winding. The space factor can be increased if the conductors or wires of the stator winding inserted in the slots are fitted to the slots.
For example, JP-A63-194543 or its counterpart application GB 2202170A discloses a stator in which portions of a coiled round wire to be inserted into slots are press-formed to have an approximately rectangular cross-section to be fitted to the slots. However, it is difficult for each layer of the press-formed wire to have a uniform cross-section and a sufficiently large space factor because a plurality of layers of the round wire is press-formed all together.
JP-A-2000-299949 or its counterpart patent U.S. Pat. No. 6,476,530 B1 discloses a stator in which U-shaped conductor segments are inserted into slots. Each conductor segments is press-formed from a round wire to have portions that have an approximately rectangular cross section except the U-shaped turn portion. However, the press-formed portions of the U-shaped conductor segments that are disposed outside the slots may receive damage during operation under a severe environmental condition.
It is a main object of the invention to provide a compact and powerful vehicle ac generator that is resistant to various environmental conditions.
According to a feature of the invention, a stator of a vehicle ac generator includes a stator core having a plurality of slots and a stator winding formed of a plurality of U-shaped conductor segments made of a wire. Each of the slots has a rectangular cross-section, and each of the U-shaped conductor segments has a U-shaped turn portion disposed outside the slots at an end of the stator core, a pair of in-slot portions extending from the turn portion and disposed in a pair of the slots and a pair of connection portions respectively welded to connection portions of other two U-shaped conductor segments. Specifically, only the in-slot portions have a press-formed approximately rectangular cross-section fitted to the slots.
Because only the in-slot portions are pressed formed, the insulation film that covers all the portions of conductor segments outside the slots are not deformed or damaged even under a sever environmental condition.